1. Field of the Invention
The present invention relates to cosmetic and dermatological light protection preparations.
2. Discussion of Background Information
The harmful effect on the skin of the ultraviolet part of the sun's radiation is generally known. Depending on their respective wavelength, the rays have different effects on the organ skin: so-called UVC radiation, with a wavelength that is less than 290 nm, is absorbed by the ozone layer in the earth's atmosphere and therefore has no physiological significance. In contrast, rays in the range between 290 nm and 320 nm, the so-called UVB range, cause an erythema, a simple sunburn or even more or less severe bums. The narrower range around 308 nm is given as a maximum of the erythema effectiveness of sunlight.
Numerous compounds are known for protection from UVB radiation, which compounds are, e.g., derivatives of 3-benzylidenecamphor, 4-aminobenzoic acid, cinnamic acid, salicylic acid, benzophenone and triazine.
It had long been wrongly assumed that long-wave UVA radiation with a wavelength between 320 nm and 400 nm has only a negligible biological effect. However, it has since been proven through numerous studies that UVA radiation is much more dangerous than UVB radiation with respect to triggering photodynamic, in particular phototoxic, reactions and chronic changes in the skin. The harmful effect of the UVB radiation can also be further increased by UVA radiation.
It is thus proven, that even UVA radiation under quite normal everyday conditions is sufficient to damage within a short time the collagen and elastin fibers that are of substantial importance for the structure and strength of the skin. This causes chronic light-related changes to the skin—the skin “ages” prematurely. The clinical picture of skin aged by light includes, e.g., wrinkles and small lines and an irregular furrowed relief. Furthermore, the parts affected by light-related skin aging can exhibit an irregular pigmentation. Also the formation of brown spots, keratoses and even carcinomas or malignant melanomas is possible. Moreover, skin prematurely aged through everyday UV exposure is characterized by a lower activity of the Langerhans' cells and a slight chronic inflammation.
Approximately 90% of the ultraviolet radiation reaching the earth is composed of UVA rays. Whereas UVB radiation varies greatly depending on numerous factors (e.g., time of year and time of day or degree of latitude), UVA radiation remains relatively constant day to day, regardless of the times of year or times of day or geographical factors. At the same time, most of the UVA radiation penetrates the live epidermis, whereas about 70% of UVB rays are stopped by the horny layer of the epidermis.
It is therefore of fundamental importance for cosmetic and dermatological light protection preparations to provide adequate protection from both UVB and UVA radiation.
In general, the light absorption behavior of light-protection filter substances is very well known and documented, especially as in most industrial nations there are positive lists for the use of such substances that apply rather strict standards for documentation.
However, the use concentration of known light-protection filter substances present as a solid is frequently limited—particularly in combination with other substances to be dissolved. Obtaining higher light protection factors or UVA protective effect thus presents certain difficulties in terms of the technical formulation.
Advantageous UVA filter substances are hydroxybenzophenones, in particular 2-[4′-(diethylamino)-2′-hydroxybenzoyl]benzoic acid hexyl ester (also: aminobenzophenone) which is characterized by the chemical structural formula:

In order to ensure optimum UV protection, these UV filter substances must be present in dissolved form. Hydroxybenzophenones are characterized by a good light-protection effect. However, their main disadvantage is that they are difficult to dissolve in conventional oil components.
Accordingly, one disadvantage of the prior art is that as a rule only comparatively low light-protection factors could be achieved with these filter substances, since their solubility or dispersibility in the formulations is too low, i.e., they cannot be incorporated into such formulations in a satisfactory manner or only with difficulty.
Even if in principle a certain UV protection can be achieved even with limited solubility, another problem often occurs: recrystallization. In particular substances that are difficult to dissolve recrystallize relatively quickly, which can be caused by temperature fluctuations or other influences. However, uncontrolled recrystallization of an essential preparation component such as a UV filter has extremely disadvantageous effects on the properties of the given preparation and—not least—on the light protection aimed for.